Bias tires having relatively narrower sectional widths had been predominantly used in vehicles until around 1960 because vehicles in those days were relatively lightweight, and the speed demanded for the vehicles were lower, resulting a less burden imposed on the tires. However, radial tires are predominant these days and those having larger widths and assuming flat shapes are particularly demanded due to increase in weight and speed of vehicles (see, for example, PTL 1).
However, the increase in a tire width sacrifices the vehicle space and thus degrades comfortability. This is a major problem particularly for electric vehicles that have been put on practical use in anticipation of future, considering situations where ensuring a space around tires has been becoming of great importance, because the electric vehicles are required to secure a space for accommodating driving components such as a motor for controlling a torque for rotating a tire about a drive shaft.
Further, there has been an increasing demand for lower fuel consumption along with increased interest in environmental issues. Here, it has been known to increase a diameter and a width of the tire in order to reduce a rolling resistance value (RR value) of the tire for better fuel efficiency. However, there is a problem that the increase in the diameter and width of the tire leads to an increase in tire weight and air resistance, which rather increases vehicle resistance and causes excessive tire loading capability.